Fiber optic sensor enclosure system

ABSTRACT

There is disclosed a sensor system comprising a sensor for detecting and signaling the presence of a fluid in an enclosure. The sensor system can be installed or incorporated within electronics and communications enclosures that house fluid-sensitive components and is useful in the early detection and warning of fluid leaks into such enclosures. In addition to the sensor, the system includes a means for conducting fluids entering the enclosure to the sensor and absorbent material to absorb any entering fluid.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/687,754, filed Jul. 25, 1996 now U.S. Pat. No. 5,712,934,priority of the filing date of which is hereby claimed under 35 U.S.C. §120.

FIELD OF THE INVENTION

The present invention relates in general to a sensor system, and moreparticularly to a sensor system that includes a fiber optical sensor fordetecting and signaling the presence of fluids.

BACKGROUND OF THE INVENTION

Briefly, fiber optic technology relates to the transmission of lightthrough a light conducting material such as optical glass, fused silica,and certain plastics. The choice of a particular material depends on theintended use of the light transmission system, and takes intoconsideration the properties of the fiber including its refractiveindex, light transmittance, as well as thermal and chemicalcharacteristics. The size (e.g., diameter and length) and configurationof the fiber optic device is also selected based on the intended use.Devices derived from light conducting materials having relatively largediameters are referred to as light pipes. In contrast, thin filamentshaving significantly smaller radii (e.g., from 100 to 3,000 micrometers,μm) are commonly referred to as optical fibers.

Known systems are designed so that light travels through an opticalfiber by total internal reflection. Light entering the optical fiber isretained by and guided through the fiber, ultimately exiting at theother end. Basically, as light is propagated through the fiber, ratherthan escaping from the fiber, light striking the surface of the fiber isreflected. The extent of light reflection at the fiber surface, andconversely the loss of light from the fiber due to refraction, is afunction of the indices of refraction of the fiber and its surroundingmedium. For example, light incident on a high-to-low refractive indexboundary (such as the interface between an optical fiber and air) at anyangle greater than the critical angle is 100% reflected at theinterface. Typical refractive indices for optical fibers range fromabout 1.2 to about 1.8, whereas the refractive index of air is 1.0003.The critical angle is a property of the light conducting material anddefined as the smallest angle with the normal to the boundary at whichtotal internal reflection occurs. Thus, for light propagated through ahigh-index material and striking the walls at greater than the criticalangle, no refractive loss of light from the fiber occurs and the lightis channeled through the fiber by total internal reflection.

In practice, despite the highly efficient transmission of light by totalinternal reflection in optical fibers, some light loss from the fiberinevitably occurs. Light losses may include, for example, refractiveloss resulting from incident light striking the fiber walls at less thanthe critical angle. Additional losses may also be attributed to opticalimpurities present within the fiber, which may scatter or absorb lighttraveling through the fiber.

In addition to the light losses noted above, the attenuation of lightintensity through an optical fiber may result from engagement of a fiberwith a medium having a refractive index approaching the index of thefiber. For example, when an optical fiber is engaged by a liquid havinga relatively high refractive index, such as water (refractive index1.33) or gasoline (refractive index 1.38), light loss from the fiber mayoccur.

Using these principles, the detection of liquid levels by fiber opticsensing is well known. Numerous fiber optic devices and methods existfor the measurement of fluid levels, such as fuel in a storage tank.Many of these devices and methods take advantage of the attenuation oflight intensity through a light-conducting medium by refractive loss asa consequence of engaging the optical fiber with a refractive mediumsuch as a liquid.

Relying on this operating principal, U.S. Pat. No. 4,187,025 to Harmerdiscloses a light guide having alternating curvatures (e.g., S- orW-shaped light guides) to produce a light signal corresponding to therefractive index of a liquid in contact with the guide. When immersed ina liquid, the alternating curvatures of the light guide providerefractive passage of an amount of light that is variable and depends onthe refractive index of the liquid. For these curvatures, the ratio ofradius of curvature to the radius of the cylindrical light guide core ispreferably between 3 and 5. The alternating curvature configuration ofthe device provides for enhanced sensitivity compared to a curvedsection bent in a single direction, such as the U-shaped devicedisclosed in U.S. Pat. No. 4,082,959 to Nakashima et al.

U.S. Pat. No. 4,287,427 to Scifres discloses several configurations of afiber optical light guide useful for detecting liquids based on thevarious liquids' indices of refraction. The disclosed configurationsinclude U-shaped and coiled light guides which, on immersion in aliquid, lose transmitted light as a function of the refractive index ofthe liquid.

A fiber optic detection system having a single fiber optic element in aU-shaped configuration and having a light variable loop section isdisclosed in U.S. Pat. No. 5,362,971 to McMahon et al. Light transmittedthrough the light variable loop section escapes from the fiber when theloop section is contacted with a medium. For this system, the higher theindex of refraction of the medium, the greater the amount of escapinglight.

The devices noted above all share the characteristic of transmittinglight through a smooth and continuous optical light guide. Opticalguides having distinct reflective and refractive surfaces have also beenemployed to measure liquid levels. U.S. Pat. No. 3,995,169 to Oddendiscloses a U-shaped light pipe having planar internal reflectingsurfaces positioned at both bends of the pipe. The planar surfaces actto reflect light from one arm of the pipe to the other arm withoutappreciable light loss when the refractive index of the surroundingmedium is less than that of the light pipe. However, when the reflectingsurfaces are immersed in a liquid, the planar surfaces become refractivesurfaces and provide for the refraction of light from the light pipe tothe surrounding liquid.

The use of reflective/refractive surfaces in optical devices to measurethe presence of a liquid in contact with the surface, such as describedabove, is well known. Many of these optical devices include suchsurfaces present in conical configurations. In these optical devices,light is transmitted to the conical tip of the light guide where lightis either: a) reflected across the tip and then returned via the lightguide to a photodetector, when the conical tip of the guide is not incontact with a refracting medium such as a liquid; or b) refracted intothe surrounding medium when the cone is immersed in a liquid. See, e.g.,U.S. Pat. No. 3,384,885 to Forbush, U.S. Pat. No. 3,535,933 to Pliml,U.S. Pat. No. 3,553,666 to Melone, U.S. Pat. No. 3,683,196 to Obenhaus,and U.S. Pat. No. 3,8321,235 to Bouton et al.

In addition to the use of refractive surfaces in cone-shaped opticaldevices, refractive surfaces have also been incorporated into fiberoptic sensors. A fiber optic probe system sensor having a refractingsurface is disclosed in U.S. Pat. Nos. 4,851,817 and 5,005,005 toBrossia et al. The disclosed optical fiber has a U-shaped configurationsimilar to those noted above for Scifres and McMahon. However, incontrast to the above-noted optical fibers, the optical fiber in Brossiaprovides a sensor portion having a rough, abraded refracting surface inthe light path. The abraded refracting surface provides an opportunityfor light to refract from the fiber and into the sensed medium. The moreabraded the fiber, the more opportunities for energy passing through thefiber to interact with the sensed medium.

The devices noted above use refractive light loss from a light guide tosense the presence of a refractive medium in contact with the guide.However, in addition to light loss from an optical fiber throughrefraction, light loss from a fiber may also occur through evanescentwave losses.

As used herein, the term "evanescent wave" refers to electromagneticradiation that results from the propagation of light through alight-conducting medium, and that is present outside of thelight-conducting medium. When light is transmitted through a high indexof refraction medium the evanescent wave (or field) is produced in theadjacent lower index of refraction material and has intensity onlywithin a fractional wavelength distance from the interface between thetwo mediums. The intensity of the evanescent wave decreasesexponentially with distance from the fiber core (i.e., E=E_(o) e⁻αrwhere E is the intensity of the evanescent wave, E_(o) is the lightintensity in the optical fiber, and α relates to the differences in theindex of refraction of the two mediums, and r is the distance from thefiber core). The presence in the field of a medium that absorbs light ofthe wavelength of the transmitted light will result in light loss fromthe fiber.

Just as for refractive light loss from optical fibers, sensors andrelated methods have been devised to exploit evanescent wave loss fromoptical fibers as a means for measuring or monitoring, for example,liquid levels in a tank or reservoir. For example, U.S. Pat. No.4,287,427 to Scifres describes a liquid-level monitor including a fiberoptic light guide having a fiber consisting of a core materialsurrounded by a cladding material. While most of the guided light isconfined to the core, a small amount of light is present in thecladding. If the cladding is removed or is sufficiently thin, theevanescent wave in the thin cladding or, in the absence of cladding,near the outer edge of the core interacts with the surrounding medium.Several configurations of the fiber optic light guide are disclosedincluding partially and fully cladded, coiled and U-shaped fibers. Forthis device, evanescent wave loss from the fiber occurs primarily whenthe wavelength of the guided light matches the absorbance wavelengths ofthe surrounding medium.

A fiber optic evanescent wave sensor system is described in U.S. Pat.No. 5,291,032 to Vali et al. The sensor system includes a light source,detector, and a cladded optical fiber having a reflector at one end. Inthe system, infrared light matching the absorbance wavelengths ofhydrocarbons, such as those present in fuels, is transmitted into thefiber. The cladding layer is sufficiently thin to permit evanescent wavelight loss to the environment. When the fiber is immersed in anabsorbing medium, evanescent wave loss occurs as a function of thelength of the fiber immersed in the liquid. The amount of light returnedto the detector by reflection from the end of the fiber is indicative ofthe depth of fiber immersion and amount of liquid present.

Accordingly, despite the number and variety of optical fiber sensors andmethods for sensing various environmental parameters, there remains aneed in the art for improved optical sensors that are highly sensitive,low cost, durable, compact, portable and suitable for fieldinstallation. The present invention seeks to fulfill these needs andprovides further related advantages.

SUMMARY OF THE INVENTION

Briefly, the present invention provides an optical sensor that uses anoptical fiber to detect the presence of a medium present in a sensedenvironment. The sensor produces a signal corresponding to the amount ofevanescent wave light loss from the optical fiber to an absorbing mediumin contact with the fiber.

In one aspect, the present invention provides an optical sensorcomprising a light source, a light detector and signal generator, and anoptical fiber extending between the light source and detector. Theoptical fiber includes a sensing length comprising a return bend in thefiber, where the return bend has a bend radius less than or equal to 2.5times the radius of the optical fiber. In a preferred embodiment, thebend radius is less than or equal to twice the radius of the opticalfiber. In one embodiment, the sensing length of the sensor's opticalfiber further includes a planar sensing surface. In a preferredembodiment, the planar sensing surface has a maximum length of abouttwice the radius of the return bend.

In another embodiment, the optical sensor further includes a signalprocessor for output signaling, and for indicating the detection of amedium in the environment.

In yet another embodiment, the optical sensor includes a beamsplitterpositioned between the light source and the sensing length to provideelectronic feedback to the light source supply to control and regulateits emission.

In still another embodiment, the optical sensor includes ananalyte-specific coating on the fiber's sensing length.

In another aspect of the present invention, a method is provided fordetecting the presence of a medium in an environment comprisingcontacting the sensing length of the optical sensor of this inventionwith the medium. The method of the present invention is useful indetecting the presence of any medium in contact with the sensor'ssensing length that absorbs light at the wavelength or wavelengthsemitted by the sensor's light source. The method of this invention isparticularly useful in detecting the presence of water, hydrocarbons,hydrocarbons in water.

In a further aspect, the present invention provides a sensing systemthat includes a sensor capable of detecting and signaling the presenceof fluid in an enclosure. The system, which may be installed orincorporated within electronics and communications enclosures that housefluid-sensitive components, is useful in the early detection and warningof fluid leaks into such enclosures. In addition to a sensor, the systemmay include a means for conducting fluids entering the enclosure to thesensor, and absorbent material to absorb any entering fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic representation of an optical sensor of the presentinvention;

FIGS. 2A and 2B are schematic representations of portions of the opticalsensor of the present invention;

FIGS. 3A and 3B are circuit diagrams for a representative optical sensorof the present invention;

FIGS. 4A and 4C are diagrammatic side elevations of sensor modules of anoptical sensor of the present invention, and FIG. 4B is a diagrammaticend elevation of the sensor module shown in FIG. 4A;

FIG. 5A is a diagrammatic side elevation of a representative moldedsensor of the present invention, and FIG. 5B is a diagrammatic endelevation of the molded sensor shown in FIG. 5A;

FIG. 6 is a schematic representation of an optical sensor of the presentinvention that includes a beamsplitter;

FIGS. 7A and 7B are diagrammatic side elevations of representativeembodiments of sensor packages in accordance with the present invention;

FIGS. 8A and 8B are schematic representations of portions of the opticalsensors of the present invention that include an analyte-specificcoating;

FIG. 9 is a graph that illustrates the sensitivity of a representativeoptical sensor of this invention in the detection of water; and

FIG. 10 is a schematic representation of a sensor system of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In one aspect, the present invention provides an optical sensor thatuses an optical fiber carrying an evanescent wave associated with aninternal beam of light. The sensor produces a signal corresponding tothe amount of evanescent wave light loss to a medium present in thesensed environment. In another aspect of the present invention, a methodfor sensing a medium present in a sensed environment is provided.

As used herein, the term "medium" refers to any substance, the presenceof which may be detected by the sensor of the present invention.Generally, the medium may be a any fluid, including a gas or liquid,that absorbs light at the wavelength(s) emitted by the sensor's lightsource. In certain instances, the medium may also be a solid havingabsorbance properties as noted above.

The term "sensed environment" refers generally to the environmentsurrounding the sensor of the present invention and includes any medium,as defined above, in contact with the sensor's sensing length and/orsensing surface.

The terms "amount of light" and "intensity of light" are usedinterchangeably and refer to the number of photons that, for example,are generated by the light source, travel through the optical fiber, arepresent in the evanescent wave, and are received at the light detector.

In general, as illustrated in FIG. 1, a first embodiment of theinvention provides a optical sensor 10 having a light source 12 forgenerating light, a light detector and signal generator 14 for receivinglight and generating variable signals dependent on the amount of lightreceived, and an optical fiber 20 extending between the light source tothe light detector and signal generator. The sensor includes a housing16 to facilitate the convenient incorporation of the sensor into anenvironment, and a signal processor 18 connected to the light detectorand signal generator for output signaling and indicating the detectionof a medium in the sensed environment.

In operation, light is transmitted from the light source 12 through theoptical fiber to the light detector 14 where a variable signal isgenerated depending on the amount of light received at the detector. Inthe absence of a light absorbing medium in the sensed environment, theamount of light received at the detector will be substantially theamount of light that is generated by the light source. In contrast, whena light-absorbing medium is present in the sensed environment, lighttransmission through the fiber will be attenuated, and the amount oflight received at the detector will be the difference between the amountof light generated by the light source and the amount of light absorbedby the medium in the sensed environment. The greater the amount of lightabsorbed by the medium, the less the amount of light received at thedetector.

Referring now to FIG. 2A, the optical fiber 20 of the optical sensor ofthe present invention has, in general, a return bend or U-shapedconfiguration that provides a guide for the light generated by thesource and received at the detector. The optical fiber has a sensinglength 26 that provides for the passage of light by evanescent wave intoa medium in contact with the sensing length. Light generated by thesource is guided through input arm 22 of the fiber to sensing length 26,and on to the detector through output arm 24. The sensing length of theoptical fiber includes the return bend portion of the fiber. In apreferred embodiment, the sensing length comprises a sharp return bend(e.g., 180°) in the fiber having a bend radius R, defined as half thedistance between input arm 22 and output arm 24 as indicated in FIG. 2A,that is less than or equal to 2.5 times the radius r of the opticalfiber core (i.e., R/r≦2.5). In a particularly preferred embodiment, thebend radius R is less than or equal to twice the radius r of the opticalfiber core (i.e., R/r≦2.0).

In another embodiment of the optical sensor of this invention, thesensor's sensing length further includes a planar sensing surface.Referring to FIG. 2B, the sensing surface 28 is located at the apexformed by the return bend in the optical fiber. A medium in contact withthe sensor's sensing length and/or the sensing surface and capable ofabsorbing light at the wavelength(s) emitted by the light source can bedetected by the optical sensor of this invention.

The sensing surface of the optical fiber is a planar optical surface.The sensing surface may be prepared by micromachining the apex of areturn bent optical fiber to provide such a planar and smooth (i.e.,optical) surface. As noted above, the optical sensor of this inventionoperates on the principal of evanescent wave sensing and, as such, thesensing surface is not a refraction/reflection surface. Rather, theplanar optical surface of the sensing surface is smooth and free fromgrooves and/or other aberrations including striations to minimizerefractive loss from the fiber. The smooth, nonrefractive sensingsurface is also located at the apex of the optical fiber bend so as tofurther minimize refraction of light from the fiber. The positioning ofthe sensing surface is such that, unlike the refracting/reflectingsurfaces of the prior art devices noted above, the sensing surface doesnot extend to the outer periphery of the bend where refraction mayreadily occur. Thus, to minimize direct refractive light loss from thefiber, the sensing surface is centered at the apex of the return bendand has one end 28a substantially aligned with the innermost edge of thelight path of the input arm 22 and the other end 28b substantiallyaligned with the innermost edge of the light path of the output arm 24.In a preferred embodiment, the sensing surface is centered at the apexof the return bend of the fiber and has a maximum length of about 2R.The position and length of a sensing surface having a length of about2R, noted by dashed vertical lines designated a and b, is shown in FIG.2B.

As noted above, the sensing surface has a maximum length of about 2R,and optical sensors of the present invention include sensors havingsensing surface lengths less than 2R. The length of the sensing surfacemay be varied depending on the sensing application. In general, thegreater the length of the sensing surface, the greater the sensitivityof the optical sensor. Preferably, the length of the sensing surface isbetween about R and 2R. It will be appreciated that as the length of thesensing surface decreases and approaches zero as the lower limit, thesensing surface becomes a point, and the sensing length of the sensor ofthe invention comprises a smooth return bend. Accordingly, in additionto optical sensors that include sensing surfaces having lengths up to2R, optical sensors having diminishingly small sensing surfaces, such asthose having a sensing length comprising a smooth return bend, are alsowithin the scope of the present invention. Nevertheless, a planarsensing surface of substantial length is preferred.

It can be demonstrated that the sensitivity of the optical sensor ofthis invention is attributable to the sharpness of the fiber's returnbend. It can also be demonstrated that the planar sensing surfacefurther enhances the sensor's sensitivity. Although not presented orintended to limit the scope of the invention, it is believed that thesharpness of the fiber's bend optimizes the evanescent wave present inthis portion of the fiber, and that the planar sensing surface coupledwith the fiber's sharp return bend further optimizes the evanescentwave. It is believed that the sharp return bend tends to concentrate thedensity of multimode reflections normal to the tangent of the apex(i.e., increase the number of reflections per unit distance along thefiber) which has the effect of creating a continuous evanescent wave (orevanescent field) along fiber's return bend apex and, when present, theplanar sensing surface. Accordingly, by virtue of its shape andconfiguration, the optical fiber of the present invention isparticularly well-suited to generating an enhanced evanescent surfacewave thereby probing a medium in contact with the sensing length and/orsensing surface. In fact, the high sensitivity of the optical sensor ofthe present invention is a direct result from the fiber's shape andconfiguration. Variations in the dimensions of the sensing surface maybe made to achieve the detection and quantitation of specific media.

The performance characteristics of the optical sensors of the presentinvention are described and summarized in Examples 2 and 3. In Examples2 and 3, the characteristics of the optical sensors of this inventionhaving R/r≦2.5 and sensing lengths comprising either a smooth returnbend or a planar sensing surface are compared to various other devicesincluding sensors incorporating straight fibers and bent fibers havingbend radii greater than 2.5. Example 2 describes the performancecharacteristics of representative sensors in the detection of water, andthe detection of oil in water is described in Example 3.

The optical fiber useful in the present invention is made of a lightconducting material. A number of suitable fibers are commerciallyavailable from a variety of manufacturers including Mitsubishi CableCo., AT&T, Belden, SIECOR, and Spectran. In the context of the presentinvention, the optical fiber includes a fiber core made of a lightconducting material and, optionally, a cladding material surrounding thefiber core. For embodiments of the optical sensors of this inventionthat employ cladded optical fibers, the cladding is removed from thefiber in the region of the sensing length. Light conducting materialsinclude any materials capable of conveying light by multiple internalreflections. Suitable materials include plastic materials, such aspolystyrene, polyacrylate, and polymethylmethacrylate materials, andglass materials such as quartz, silica glass, borosilicate glass, leadglass, and fluoride glass materials. Preferred optical fibers includeplastic fibers having diameters from about 250 to about 2000 μm, andglass fibers having diameters from about 50 to about 250 μm. Suitableoptical fibers are essentially transparent to the wavelength(s) of lightgenerated by the light source, may be either single or multimode fibers,and may include fibers having specific transmission modes and wavelengthbands. In a preferred embodiment, the optical fiber is a multimodeplastic fiber having a diameter of 1000 μm, such as commerciallyavailable from Mitsubishi Cable America, Inc., New York, N.Y. (Eska™).

The light source of the optical sensor serves to generate light, and maybe selected based on the sensing application where the source's outputwavelength is matched with the wavelength of absorbance of the medium tobe sensed. In a preferred embodiment, the light source emits light at awavelength or wavelengths in the red and/or near-infrared region of thespectrum, i.e., from about 600 to about 1500 nm. In general, lightsources useful in the optical sensor of this invention include tungstenlight sources, light-emitting diodes, and laser diodes. Suitable laserdiodes include diodes composed of gallium arsenide (GaAs) and aluminumgallium arsenide (AlGaAs) materials, which are electroluminescent andemit in the near-infrared (i.e., 1050 and 1150 nm, respectively). Othersuitable light sources include light-emitting diodes having peakemission wavelengths at, for example, 850 nm, 880 nm, 940 nm (availablefrom Clairex Technologies, Plano, Tex., as models CLC216PR, CLC211PR,and CLC112PR, respectively), 950 nm, and 1300 nm (available from SiemensOptoelectronics, Inc., as models SFH450 and STL51007G, respectively). Ina preferred embodiment, the light source is a light-emitting diodehaving a wavelength of emission centered at about 950 nm, commerciallyavailable from Siemens Optoelectronics, Inc.

The light detector and signal generator of the optical sensor receiveslight from the light source and generates variable signals dependent onthe amount of light received at the detector. Suitable light detectorsinclude any photodetector, such as a photodiode or phototransistor,capable of responding to light emitted from the light source.Preferably, the light detector has a photosensitivity (i.e.,photoresponse) over at least the bandwidth of the source's emissionwavelengths. Light detectors useful in the optical sensor of thisinvention include, for example, models SFH350 and the SRD0021x seriesphotodetectors commercially available from Siemens Optoelectronics Inc.,and models CLC400 CLC600 series photodetectors available from ClairexTechnologies. In a preferred embodiment, the light detector is aphototransistor, such as model SFH350, commercially available fromSiemens Optoelectronics Inc. As noted above, the optical sensor may alsoinclude a signal processor connected to the light detector and signalgenerator to process and output signals from the signal generator toindicate the presence of a selected medium in the environment.

The electronic components of a representative optical sensor of thisinvention are shown in the circuit diagrams of FIGS. 3A and 3B. Withreference to FIGS. 3A and 3B, power for the light emitting diode D2 canbe provided by a constant current source 102 based on a three terminaladjustable regulator 104, such as a National Semiconductor LM317LZ.Regulator 104, in turn, receives input power (12 volts DC) through aninput filter R1, C1. For the photodetector D1 and the signal processingcircuit 106, power is supplied by a voltage source 108 which also can bebased on a three terminal adjustable regulator 110 (LM317LZ) receivingpower (12 volts DC) through the input filter R1, C1. The output from thephotodetector is applied to a voltage divider R7, R8, with the maximumvoltage across resistor R8 limited by a Zener diode CR1. The voltageacross resistor R8 is filtered by a two-stage filter R9, C2 and R10, C3,before being amplified by a chopper-stabilized operational amplifiercircuit (U3:A). The processing circuit then subtracts a referencevoltage (found at the junction of R14 and R15) from the amplifiedvoltage, and further amplifies the voltage difference at anotheroperational amplifier (U3:B). This amplified, offset voltage is theoutput.

The optical sensor may include a housing to form a sensor module tofacilitate the convenient incorporation of the sensor into anenvironment. The housing for the optical sensor may take any one of avariety of forms depending on the sensing application. For example, thehousing may be a cylindrical sleeve of plastic and/or metal thatsurrounds the optical fiber and seals the light source and detector, aswell as the signal generator and processor, from the sensed environment.In the sensor module, the sensing length of the optical fiber is exposedto the environment for sensing of a selected medium. Alternately, thehousing may be a sensor sleeve, such as described above, furtherincluding a threaded surface such that the sensor may be inserted andsecured into an environment by a threaded sensor receiving means.Representative sensor modules are illustrated in FIGS. 4A and 4C.

The housing used to form the sensor module may, under certaincircumstances, impose the bend radius in the optical fiber useful in thesensor of the present invention. For example, in one embodiment, thesensor module housing is a cylindrical sleeve having an outer diameterof about 0.2 inches (with a nominal wall thickness of about 0.02inches). The use of a 1000 μm (0.04 inch) diameter optical fiber in areturn bend configuration with such a housing results in a separation ofabout 0.08 inches (R=0.04 inch) between the input and output arms of thefiber. In such a configuration, the bend radius R (0.04 inch) is equalto twice the fiber radius r (0.02 inch), i.e., R/r=2.0. Such aconfiguration is distinguished from the configurations of the prior artsensors noted above that contain bent optical fibers having R/r>>2.

Referring to FIG. 4A, in one embodiment the sensor module 30 has acylindrical body 32 that encompasses optical sensor 10. In thisembodiment, the input and output arms of optical fiber 20 are enclosedin housing 16, and sensing length 26, including optional sensing surface28, extend from the housing to permit engagement of the sensing surfacewith a medium present in the sensed environment. In an embodiment ofthis sensor module, the cylindrical body 32 extends to a length of atleast the outer reach of sensing length 26 and optional sensing surface28, and further provides channels 34 in cylindrical body 32 as a meansfor permitting the engagement of a medium with sensing surface 28. Anend elevation of the sensing end of the sensor module depicting sensingsurface 28 and channels 34 is shown in FIG. 4B. A sensor module 30having a threaded body 36 that encompasses optical sensor 10 is shown inFIG. 4C. As noted above for the sensor module having a cylindrical body,sensing length 26 and optional sensing surface 28 may either extend fromor be recessed in threaded body 36. In embodiments having a recessedsensing surface, the threaded body may include channels for theengagement of a medium with the sensing surface.

In a preferred embodiment, the optical sensor of the present inventionis a molded sensor made of a plastic light conducting material such aspolymethyl methacrylate. The molded sensor includes the optical sensorcomponents noted above (e.g., the light guide having a sensing length,the light source, and the light detector) where the source and detectorare fitted into the plastic mold. A representative molded sensor isillustrated in FIG. 5A. Referring to FIG. 5A, the light source 12 andlight detector and signal generator 14 of molded sensor 40 are locatedin cylindrical body 42 of the molded sensor. Extending from thecylindrical body 42 are input arm 22, sensing length 26 includingsensing surface 28, and output arm 24. An end elevation of the moldedsensor is shown in FIG. 5B.

The molded sensor offers the advantage of ease of production includingthe uniform manufacture of the return bend and, optionally, the planaroptical surface of the fiber's sensing length. An additional advantageof the molded sensor is that no leakage of liquid from the environmentinto the sensor can occur.

In one embodiment, the optical sensor includes a beamsplitter positionedin the path of the light generated by the source. Referring to FIG. 6,in one embodiment the sensor has beamsplitter 50 positioned along inputarm 22 between light source 12 and sensing length 26. The beamsplitterdirects a portion of the generated light to a second light detector andsignal generator 52 such that the intensity of the light generated bythe source may be monitored. The beamsplitter and associated secondlight detector and signal generator provide a means for calibrating theintensity of the source and allow for the quantitation of the amount oflight loss from the sensing length of the optical fiber by comparing theamount of light received at light detector 14 and the second lightdetector.

Alternatively, a phototransistor may be positioned directly along inputarm 22 to provide electronic feedback to the light source supply tocontrol and regulate the intensity of the light emitted from the source.

The optical sensor of the present invention may be employed in a numberof configurations and sensing environments to monitor and reportconditions and changes in conditions measurable by the sensor. As notedabove, to best sense the presence of a particular medium, the sensor'slight source emission wavelength or wavelengths should overlap to atleast some extent with the absorbance wavelengths of the medium soughtto be detected. In the context of the present invention, sensors havinglight sources emitting red and near-infrared wavelengths areparticularly useful in detecting the presence of water and hydrocarbonssuch as fuels including gasoline and oil. As used herein, the term"hydrocarbon" refers to a substantially organic compound that includescarbon-hydrogen (i.e., C--H) bonds.

The sensor of the present invention may be located in certainenvironments where, for example, the presence of water may be hazardousto the smooth functioning of certain components such as electricalcomponents present in an electrical box. In such an application, asensor may be installed in the box in such a position that any waterthat finds its way into the box ends up in contact with the sensinglength and/or sensing surface of the sensor. In the event that waterdoes collect and contacts the sensing length and/or sensing surface, theattenuation of light through the optical fiber of the sensoraccompanying the contact of water results in the generation of an outputsignal indicating the presence of water in the electrical box. Notice ofthe presence of water in the box allows for action to be taken toservice the particular box and avoid any costly damage that would resultfrom unnoticed and unattended accumulation of water in the box.

Thus, in another aspect, the present invention provides a sensor systemthat includes a sensor capable of detecting and signaling the presenceof fluid in an enclosure. The system can be integrally formed with orinstalled within an enclosure that contains one or more fluid-sensitivecomponents including, for example, electronic and communicationsconnections or splices. In accordance with the sensor system, fluidentering the enclosure is conducted to the sensor which detects thepresence of the fluid and transmits a signal via a communications lineto a communications control center. Upon receipt of this information,action may be taken to service the enclosure and thereby prevent damageto the fluid-sensitive component(s) housed within the enclosure. Becausethe sensor generates a signal in advance of fluid entering that portionof the enclosure housing the fluid-sensitive component(s), a promptresponse to the sensor's signal can avoid costly damage to the enclosedcomponents.

The sensor system of the present invention is particularly useful inconnection with splice closure systems. The term "splice closure system"generally refers to a device that encloses electronic and/orcommunication cable splices (i.e., connections) including fiber opticsplices, mechanical and fusion splices, which are useful in a variety ofapplications including aerial, building, direct buried and undergroundapplications. Splice closure systems are well known in the art and maytake any one of a number of forms or configurations. Generally, spliceclosure systems are designed to protect sensitive electronic andcommunication splices from damage that may otherwise result fromexposure to hostile environmental conditions including temperatureextremes, sunlight, wind, and precipitation such as rain, sleet, andsnow. Among other protections, these closure systems seek to preventmoisture from entering the closure and causing damage to thewater-sensitive components contained within the enclosure. The sensorsystem of the present invention can be incorporated into a spliceclosure system to provide a means for monitoring moisture within such aclosure.

As noted above, the sensor system can be integrally formed with orinstalled within an enclosure that houses fluid-sensitive components.The sensor is preferably incorporated into the enclosure in a positionsuch that a fluid entering the enclosure contacts the sensor prior totraveling to and potentially damaging the enclosure's fluid-sensitivecomponent(s). In addition to the sensor, the system preferably includesa means for conducting any fluid entering the enclosure to the sensorand an absorbent material to absorb any fluid entering the enclosure.

A schematic illustration of a representative sensor system associatedwith a typical enclosure for housing fluid-sensitive components (i.e., asplice closure system) is shown in FIG. 10. The splice closure systemdepicted in FIG. 10 is a common closure configuration having input andoutput cables extending from one end of the closure. It will beappreciated that other closure configurations, including closures havinginput and output cables extending from opposite ends of the closure, arewithin the scope of the present invention and would benefit from theadvantages afforded by sensor system of this invention. In such anembodiment, the closure can include two sensor systems, corresponding toeach cable port, located near each end of the closure. It will also beappreciated that, depending on the particular closure system, theclosure can include any one of a variety of means for securing andsealing the closure's cover to the closure's base. One such means, aclamp and O-ring seal, is illustrated in FIG. 10.

Referring to FIG. 10, the illustrated splice closure system generallyincludes base 102, dome 104, splice organizer tray 106, O-ring seal 108,and clamp 110. Clamp 110 secures dome 104 to base 102 and provides aseal through O-ring 108. The O-ring forming the dome/base seal ispreferably made from a water impervious elastomeric material. Dome 104further includes ports 112 for receiving input (i.e., feeder) and output(i.e., distribution) cables. The cables are organized and spliced in theclosure on tray 106.

As shown in FIG. 10, the representative sensor system includes sensor120, a fluid conducting means 122 (or 124 shown in broken line), andabsorbent barrier 126. In a typical splice closure system, the sensor ispowered from a source associated with either the input and/or outputcables, and the sensor signals the presence of fluid in the closurethrough a communication line, for example, optical fibers associatedwith the cables noted above.

The sensor is generally positioned between the closure's primary sealand the closure's fluid-sensitive components. Referring again to FIG.10, when dome 104 is secured to base 102, sensor 120 is positionedbetween O-ring 108 and absorbent barrier 126. In the embodimentillustrated in FIG. 10, absorbent barrier 126 is a ring-shaped barrierin communication with the interior surface of base 102 and having anaperture of size sufficient to permit tray 106 to pass unimpeded intothe closure's base. Barrier 126 is a continuous ring mounted in theclosure base and includes an absorbent material, preferably asuperabsorbent polymeric material. In its sealed configuration,absorbent barrier 126 is positioned between sensor 120 and the closure'sfluid-sensitive components located on tray 106. As a result of thisconfiguration, any fluid entering the closure through the dome/baseconnection is first directed by a conducting means to the sensor, whereit is detected. and its presence signalled. Any fluid migrating beyondthe sensor and toward the fluid-sensitive component located on tray 106is intercepted and absorbed by the absorbent barrier. Thus, barrier 126provides the closure with a measure of protection during the period oftime between the sensor's initial signaling of the presence of fluid inthe closure and servicing of the closure.

Suitable sensors useful in the system of the present invention includeany sensor capable of detecting and signaling the presence of a fluid,for example, water or moisture. Preferably, the sensor is an opticalsensor such as a sensor of the present invention described above.

Generally, the sensor is positioned in the enclosure to be sensed suchthat any fluid that enters the enclosure collects at or near the sensorfor ready detection. Accordingly, the sensor is generally positioned atthe enclosure's lowest point, for example, at the lowest point of theenclosure's floor. The fluid conducting means can include any one of anumber of means including, for example, a fluid conduit and otherrouting means. As shown in FIG. 10, a preferred means for conducting afluid to the sensor is helical groove 122 (i.e., a "racetrack"), whichencircles the interior circumference of base 102 between O-ring 108 andsensor 120. In another preferred embodiment, the fluid conducting meansis flange 124 extending inwardly from the interior surface of base 102and in communication with sensor 120. Fluid entering the closure andtravelling toward the sensor encounters flange 124 and is conducted tothe sensor.

Employing the advantages offered by the sensor of the present inventionwith regard to the sensor's ability to detect the presence ofhydrocarbons such as fuels in water, the sensor may be incorporated intoa sensor package, such as a flotation device, and located in bodies ofwater (e.g., rivers, streams, ponds, and lakes) to detect fuel spills.An example of such an embodiment is illustrated in FIG. 7A. Referring toFIG. 7A, sensor module 30 is positioned in a flotation device 70 made ofbuoyant material. Flotation device 70 is designed to float on a liquidsurface and permit contact of sensing length 26 and/or sensing surface28 with the surface of the liquid.

The sensor of the present invention may also be incorporated into asensor package useful as a liquid level monitoring device. In oneembodiment, a plurality of sensor modules may be embodied to determinethe level of a particular fluid such as the level of water in a storagetank, the level of fuel in a fluid tank, or the level of a liquid suchas water or oil in a well site. An example of such a sensor package isillustrated in FIG. 7B. Referring to FIG. 7B, sensor modules 30 areadjacently positioned in liquid level monitoring device 80 such thatwhen the liquid level is sufficient to immerse a portion of the device,one or more of sensing lengths 26 and/or sensing surfaces 28,corresponding to the portion of the device immersed in the liquid,contacts the liquid medium and generates a signal which is sent tosignal processor 18. Monitoring device 80 may optionally includeshutters 82 which may be controlled so as to open and allow for thesampling of an environment once the monitoring device has beenpositioned in the particular environment.

In another embodiment, the optical sensor further includes ananalyte-specific coating. This embodiment renders the sensor useful inmeasuring specific analytes (e.g., chemicals and biochemicals) that maybe present in a medium, as well as medium parameters including pH andionic strength. As used herein, the term "analyte-specific coating"refers to a deposit or coating of a material onto either the opticalfiber's sensing length or the fiber's sensing surface. The deposited orcoated material interacts with a specific analyte present in a mediumand the interaction is measurable by the sensor of the presentinvention. Basically, the interaction between the analyte-specificcoating of the sensor and the specific analyte present in the solutionresults in some change that is measurable by the evanescent waveproduced by the sensor of the present invention. Operationally, oncontacting the analyte-specific coating with a medium containing ananalyte that specifically interacts with the coating, light loss fromthe fiber occurs in an amount directly proportional to the amount ofspecific analyte interacting with the analyte-specific coating. Thus,the presence and, if calibrated, the quantity of a specific analytepresent in a medium may be determined.

Referring to FIGS. 8A and 8B, analyte-specific coating 60 is applied toand located on the optical sensor's sensing length 26 and sensingsurface 28, respectively.

As noted above, the interaction between any two materials that resultsin a change in the amount light lost from the optical fiber may besuitably measured by the sensor of the present invention. Theanalyte-specific coating may be a chemical such as an indicatorcompound; a biochemical or biological molecule such as an enzyme,antibody, or nucleic acid; or a membrane that selectively binds aparticular chemical or biochemical. Suitable chemical coatings include,for example, organic and inorganic compounds that, on exposure to amedium containing certain other chemicals, biochemicals, or metal ions,undergo a change in their absorbance properties. The use of specificbiochemical binding partners or specific binding pairs, includingreceptor molecules and their ligands, antibodies and their ligands, andcomplementary nucleic acid sequences, are also within the scope of thisembodiment of the present invention. In such embodiments, one member ofthe specific binding pair (e.g., a receptor) may serve asanalyte-specific coating to detect as the analyte, the other member ofthe pair (e.g., its ligand). Synthetic membranes that undergo changes intheir absorbance properties in response to parameters of a medium, suchas pH, ionic strength, or the presence of certain chemicals includingmetal ions and dissolved gases such as oxygen and carbon dioxide, andbiochemicals including biological species, may also be useful asanalyte-specific coatings in the sensor of this invention.

In another aspect of the present invention, a method of detecting amedium in an environment is provided. In the method, a medium isdetected by contacting the sensing length and/or sensing surface of theoptical sensor described above with the medium. When the medium incontact with the sensing length and/or sensing surface absorbs light atthe wavelength(s) emitted by the light source, light transmissionthrough the optical fiber is attenuated and the amount of light receivedat the detector is decreased in an amount proportional to the nature andamount of the medium sensed relative to the light received in theabsence of the absorbing medium.

Optical sensors of the present invention that employ broadband lightsources and a multimode waveguides are useful in detecting any fluidthat has an absorbance band within the bandwidth of the sensor definedby the emission bandwidth of the sensor's light source. The term"broadband light source" refers; to the band of wavelengths emitted bythe sensor's light source. The term "multimode waveguide" refers to thecapacity of the light conducting material of the input arm, sensinglength, and output arm of the sensor to transmit light of all phases.

The characteristics of the optical sensor of the present inventionrender methods for detecting substances that absorb in the red and/ornear-infrared region of the spectrum particularly effective. Forexample, when the medium sought to be detected is water (or a primarilyaqueous medium), the use of a light source emitting at about 850 nm iseffective in detecting as little as 0.1 μL of water present on thesensor's sensing surface. FIG. 9 graphically illustrates the decrease inoutput signal of a representative optical sensor of this invention as afunction of the volume of water in contact with the sensor's planarsensing surface. The sensitivity of representative optical sensors ofthis invention in the detection of water is presented in Example 2.

The high sensitivity of the method is due to the unique configuration ofthe sensor of this invention, and also due to the broadband absorbanceof water in the near-infrared region of the spectrum. The method takesadvantage of the broad near-infrared absorbance of water with thewavelength(s) of light generated by sensor source. The absorbance ofwater increases greatly from about 400 nm and continues to increase intothe far infrared beyond 4000 nm. Thus, the most sensitive methods fordetecting water utilizing the sensor of this invention employwavelengths of light in water's broad absorbance band (i.e., thewavelength(s) at which the greatest amount of the evanescent waveproduced by the sensor is absorbed by water in contact with the sensingsurface).

As shown in Table 1 of Example 2, the effective detection of water isachieved by the optical sensors of this invention having return bendswith R/r about 2.0. For the sensor having a smooth return bend (seeTable 1, entry 8), a 58% decrease in output signal was observed when thesensing length was contacted with water. The result demonstrates thatthe return bend with R/r about 2 is responsible for the high sensitivityachieved by the sensors of the present invention. As indicated in Table2 of Example 2, the onset of the sensor's high sensitivity occurs whenR/r is decreased to less than about 2.5. A dramatic decrease in outputsignal (87%) was observed for the sensor having a planar sensing surface(see Table 1, entry 9). The result demonstrates that the highsensitivity achieved by the sensors of this invention having a returnbend with R/r<2.5 is further enhanced by the presence of the sensingsurface located on the apex of the return bend.

Sensitive methods for detecting hydrocarbons, such as those contained infuels, also exploit the strong absorbances of these substances in thenear-infrared region of the spectrum. The near-infrared absorbances aredue to C--H bonds present in all hydrocarbons. Typical near-infraredabsorbance bands for these substances occur at about 1200 nm (1.2 μm )and 1400 nm (1.4 μm) and have bandwidths of about 50 nm. Accordingly,the most sensitive methods for detecting hydrocarbons utilizing thesensor of this invention employ sources emitting light at or near thesewavelengths.

Where it is desirable to detect the presence of a substance in anenvironment, the most sensitive method employs a wavelength of lightunique to that substance, i.e., a selective sensor. However, if thedetection of a particular class of substances is desired, the methodshould employ a wavelength band common to all substances in the class.If the detection of one substance in the presence of another is desired,and each has a unique wavelength of absorbance, then either may bedetected in the presence of the other by appropriate wavelengthselection. The use of a common absorbance wavelength may be successfulwhen one substance absorbs more strongly at the wavelength than theother. In such an instance, the method may utilize a wavelength wherethe substance present in the lowest amount has the greatest absorbancerelative to the absorbance for the predominant substance.

In addition to detecting a substance such as water or a hydrocarbon, themethod of the present invention may also be useful in detecting onesubstance in the presence of another, for example, detecting a substancepresent in a medium, such as a hydrocarbon in water. The method utilizesthe sensor of this invention employing a light source emitting at awavelength of light commonly absorbed by both substances, but morestrongly absorbed by the hydrocarbon. In a preferred embodiment, themethod utilizes the sensor of this invention employing a light sourceemitting at about 950 nm.

The effective and sensitive detection of oil in water by the sensor ofthis invention is shown in Table 3 of Example 3. In these experiments,the sensors were contacted with the surface of water upon which wasdispersed 6×10⁻⁴ μL oil per square millimeter. As observed in the watersensitivity experiments, no significant output signal decrease wasobserved for sensors having optical fibers with return bends whereR/r>2. However, a significant decrease in signal was observed for thesensors of the present invention having R/r=2.0. For the representativesensor having a smooth return bend, a signal decrease of about 85% wasobserved (see Table 3, entry 8). A 10-fold greater decrease in signal, adecrease of about 98%, was found for the representative sensor having asensing surface at the apex of the return bend (see Table 3, entry 9).

These results indicate that the sensors of the present invention areuseful in detecting the presence of one fluid, an oil or fuel, in thepresence of another, water. Such usefulness is unique to the opticalsensors of the present invention and is a distinguishing characteristicover the known optical sensors noted above.

The following examples are offered by way of illustration, notlimitation.

EXAMPLES Example 1 The Manufacture of a Representative Optical Sensor

In this Example, the manufacture of a representative optical sensor ofthe present invention is described. As noted above, the optical sensorincludes a light source, a light detector and signal generator, anoptical fiber, and a signal processor. The signal processor is anelectronic circuit having the components arranged on a circuitboard in aconfiguration as described above and as shown in the circuit diagram inFIGS. 3A and 3B. The sensor is assembled by preparing the optical fiber,mounting one end of the fiber into the light source (i.e., the photocellor light-emitting diode), mounting the other end of the fiber into thelight detector, securing the fiber to the source and detector throughthe use of either black adhesive tape or heatshrink tubing, andsoldering the light source and light detector on the circuitboard asindicated in the circuit diagram. Depending upon the particularapplication, the assembly including optical fiber, light source anddetector, and circuitboard may be installed in a suitable housing.

The optical fiber is prepared by cutting a piece of fiber to the desiredlength and polishing its ends. The cladding is then removed from thefiber over the sensing length portion of the optical fiber. The fiber isthen bent into the desired return bend configuration by warming andbending around a cylinder having the desired bend radius. If the opticalsensor is to include a sensing surface, the sensing surface is preparedby machining the optical fiber such that a planar surface is formed atthe apex of the return bend of the optical fiber.

To evaluate the performance characteristics of the sensors of thisinvention, representative optical sensors were assembled as describedabove. The sensors included a 1000 μm (0.04 inch, r=0.02 inch) diameterpolymethylmethacrylate optical fiber (AMP Optimate), a light-emittingdiode having a peak emission at 950 nm (SFH450, Siemens Optoelectronics,Inc.), and a phototransistor (SFH350, Siemens Optoelectronics, Inc.),and accompanying electronic circuitry as shown in FIGS. 3A and 3B. Forthe optical sensor having a sensing surface, a planar surface having alength of 0.040 inch was prepared by machining the apex of the returnbend of the fiber. The performance characteristics of the representativeoptical sensors assembled from the components noted above are presentedin Examples 2 and3.

Example 2 Performance Characteristics of Representative Optical Sensors:Water Sensitivity

In this Example, the performance characteristics of representativeoptical sensors prepared as described above in Example 1 are summarized.The sensitivity of the optical sensors in detecting water was comparedto other optical fiber-based sensing devices having identical lightsource, detector, and signal processor, and differing only in theconfiguration of the optical fiber (i.e., bend radius and sensingsurface). The water sensitivity of each of the sensors was determined byimmersing the sensing length of each in water. The sensing length foreach was prepared by removing the cladding on a 0.7 inch portion of thefiber. The signal-processing circuit was set for a regulated 6.5 voltsDC supply with a 5.0 volt output of the sensor. For each sensor outputsignal measurements were made in air, water, and again in air afterdrying subsequent to water immersion. The results are summarized inTable 1.

                  TABLE 1                                                         ______________________________________                                        Sensitivity of sensor output signal as a function of                          optical fiber configuration: water detection                                          Bend                                                                          Radius        Output Signal Signal                                            R             (volts)       Decrease                                  Configuration                                                                           (inches)                                                                              R/r     Air  Water Dry  (%)                                 ______________________________________                                        1 no bend --      --      5.00 5.00  5.00 --                                  2         1.33    66.5    5.00 5.00  5.00 --                                  3         0.41    20.5    4.98 4.98  4.98 --                                  4         0.28    14.0    4.97 4.96  4.97 <1                                  5         0.25    13.0    4.97 4.96  4.97 <1                                  6         0.15     7.5    4.95 4.92  4.95 <1                                  7         0.10     5.0    4.93 4.87  4.92 1.2                                 8 smooth bend                                                                           0.04     2.0    4.91 2.08  4.91 58                                  9 sensing surface                                                                       0.04     2.0    4.80 0.63  4.80 87                                  ______________________________________                                    

The results in Table 1 show that the representative optical sensors ofthe present invention having R/r=2.0 were the most sensitive sensors.The results demonstrate that the sharp return bend of the optical fiberof the sensors of the present invention are critical in providing ahighly sensitive sensor for detecting water.

Referring to Table 1 above, less than a 1% decrease in output signal wasobserved until the optical fiber bend radius was decreased to a value ofR/r of about 7.5. A decrease in R/r to 5.0 provided only a 1.2% decreasein output signal. A dramatic decrease in output signal of about 58% wasobserved for a representative sensor of the present invention withR/r=2.0 (see Table 1, entry 8). Furthermore, the representative opticalsensor having a planar sensing surface provided enhanced sensitivitycompared to the sensor having a smooth return bend. On contact withwater, the decrease in output signal for the sensor having a planarsensing surface was observed to be about 87% (see Table 1, entry 9).

The stability of the sensor of this invention is demonstrated by theoutput signal observed after blow drying the fiber. In each case, theoutput signal returned to its original value in air indicating that thesensor may be reliably used to continuously monitor changes in itsenvironment.

To more closely examine the effect of sensor configuration, particularlythe sensitivity of bend radius (i.e., R/r) on the sensors' detection ofwater, the output signal for several optical fiber configurations, eachhaving a smooth bend, was measured as described above. The results aresummarized in Table 2.

                  TABLE 2                                                         ______________________________________                                        Sensitivity of sensor output signal as a function of                          optical fiber configuration: water detection                                                                     Signal Decrease                            Configuration                                                                            R/r      Air    Water   (%)                                        ______________________________________                                        1          3.25     4.86   4.77    1.9                                        2          3.05     4.83   4.70    2.7                                        3          2.75     4.82   4.66    3.3                                        4          2.50     4.73   3.68    22                                         ______________________________________                                    

The results of Table 2 demonstrate that the sensor output signaldecreases dramatically with R/r and that high sensor sensitivity onsetoccurs at about R/r=2.50. Accordingly, the optical sensors of thepresent invention have R/r≦2.50, and preferably R/r about 2.0.

Example 3 Performance Characteristics of a Representative OpticalSensor: Oil in Water Sensitivity

In this Example, the performance characteristics of representativeoptical sensor of the present invention in detecting the presence of oilin water are described. The optical sensors used in this Example wereprepared as described in Examples 1 and 2 above. An oil-in-water mixturewas prepared by dropping 20 μL of oil (SAE 30 motor oil) into acontainer filled with water and having a surface area of about 33,000mm² and allowing the oil to spread over the surface of the waterovernight. The sensing length for each optical fiber for each sensor wascontacted with the water's surface and the signal output recorded. Theresults are presented in Table 3.

                  TABLE 3                                                         ______________________________________                                        Sensitivity of sensor output signal as a function of                          optical fiber configuration: oil in water detection                                   Bend Radius    Output Signal                                                                              Signal                                            R              (volts)      Decrease                                  Configuration                                                                           (inches)  R/r    Air  Oil/Water                                                                             (%)                                   ______________________________________                                        1 no bend --        --     5.01 5.01    --                                    2         1.33      66.5   5.01 5.01    --                                    3         0.41      20.5   4.99 4.99    --                                    4         0.28      14.0   4.99 4.99    --                                    5         0.25      13.0   4.99 4.99    --                                    6         0.15       7.5   4.97 4.98    --                                    7         0.10       5.0   4.97 4.88    1.8                                   8 smooth bend                                                                           0.04       2.0   4.87 0.51-0.90                                                                             86                                    9 sensing surface                                                                       0.04       2.0   4.80 0.013-0.065                                                                           99                                    ______________________________________                                    

The results in Table 3 show that the most sensitive detection of oil inwater is achieved using the representative optical sensors of thepresent invention having R/r=2.0. A dramatic decrease in the signaloutput (on average about an 86% decrease) is observed for the opticalsensor of the present invention having a smooth return bend (see Table3, entry 8) compared to the other sensors having greater bend radii. Theobserved decrease is also significantly greater than that observed whenthe sensor was contacted with water alone as shown in Example 2, Table1, entry 8. The optical sensor having a planar sensing surface (seeTable 3, entry 9) shows about a tenfold greater change in signal output(on average about a 99% decrease) upon contact with the oil-in-watersurface as compared to water alone. The large decreases in output signalnoted above were observed by contacting the sensor's sensing length withthe water's surface upon which was dispersed about 6×10⁻⁴ μL oil persquare millimeter. These results illustrate that the sensitivity of theoptical sensors in detecting oil in water is significantly greater thantheir sensitivity to water alone, and thus the sensors are ideal formonitoring the presence of oils in water and useful in continuousmonitoring of ground water or water supplies for contamination byhydrocarbons such as fuels and oils.

While the preferred embodiment of the invention has been illustrated anddescribed, it will be appreciated that various changes can be madetherein without departing from the spirit and scope of the invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A sensor systemcomprising:an enclosure for a fluid-sensitive cable connection, theenclosure having input and output ports for receiving input and outputcables extending from the fluid-sensitive connection within theenclosure, through the ports to the outside of the enclosure; and afluid sensor positioned in the enclosure for detecting and signaling thepresence of a fluid within the enclosure, wherein the fluid-sensitiveconnection is selected from the group consisting of electronic andcommunication connections.
 2. A sensor system comprising:an enclosurefor a fluid-sensitive component; and a fluid sensor positioned in theenclosure for detecting and signaling the presence of a fluid within theenclosure, wherein the fluid-sensitive component is selected from thegroup consisting of electronic and communication connections; andwherein the enclosure comprises a means for conducting fluid to thesensor.
 3. The sensor system of claim 2 wherein the means for conductingfluid to the sensor is a groove.
 4. The sensor system of claim 2 furthercomprising an absorbent material in the enclosure and positioned toabsorb fluid to protect a fluid-sensitive component in the enclosure. 5.The sensor system of claim 4 wherein the absorbent material comprises asuperabsorbent polymeric material.
 6. The sensor system of claim 2wherein the sensor is an optical sensor, comprising:(a) a light sourcefor generating light; (b) a light detector and signal generator forreceiving light from the light source and for generating variablesignals dependent on the amount of light received; and (c) an opticalfiber made of a light conducting material extending between the lightsource and the light detector and having a sensing length comprising areturn bend in the optical fiber forming an apex, wherein the returnbend has a bend radius less than or equal to about 2.5 times the radiusof the optical fiber.
 7. The sensor system of claim 2 wherein the sensoris an optical sensor, comprising:(a) a light source for generatinglight; (b) a light detector and signal generator for receiving lightfrom the light source and for generating variable signals dependent onthe amount of light received; and (c) an optical fiber made of a lightconducting material extending between the light source and the lightdetector and having a sensing length comprising a return bend in theoptical fiber forming an apex, wherein the return bend has a bend radiusless than or equal to about 2.5 times the radius of the optical fiber,wherein the sensing length further comprises a planar sensing surface atthe apex of the return bend, and wherein the planar sensing surface hasa maximum length of about twice the radius of the return bend.
 8. Asensor system comprising:an enclosure; a fluid-sensitive componentmounted in the enclosure; and a fluid sensor positioned in the enclosurefor detecting and signaling the presence of a fluid within theenclosure, wherein the fluid-sensitive component is selected from thegroup consisting of electronic and communication connections; andwherein the enclosure comprises a means for conducting fluid to thesensor.
 9. The sensor system of claim 8 wherein the enclosure isnormally fluid-tight, the fluid-sensitive component being a cablesplice, the enclosure being adapted for mounting the cable splicetherein.
 10. The sensor system of claim 9 further comprising anabsorbent material mounted in the enclosure and positioned to absorb thefluid to protect the cable splice.
 11. The sensor system of claim 10wherein the absorbent material comprises a superabsorbent polymericmaterial.
 12. The sensor system of claim 10 wherein the fluid is water.13. The sensor system of claim 9 wherein the sensor is an opticalsensor, comprising:(a) a light source for generating light; (b) a lightdetector and signal generator for receiving light from the light sourceand for generating variable signals dependent on the amount of lightreceived; and (c) an optical fiber made of a light conducting materialextending between the light source and the light detector and having asensing length comprising a return bend in the optical fiber forming anapex, wherein the return bend has a bend radius less than or equal toabout 2.5 times the radius of the optical fiber.
 14. The sensor systemof claim 9 wherein the sensor is an optical sensor, comprising:(a) alight source for generating light; (b) a light detector and signalgenerator for receiving light from the light source and for generatingvariable signals dependent on the amount of light received; and (c) anoptical fiber made of a light conducting material extending between thelight source and the light detector and having a sensing lengthcomprising a return bend in the optical fiber forming an apex, whereinthe return bend has a bend radius less than or equal to about 2.5 timesthe radius of the optical fiber, wherein the sensing length furthercomprises a planar sensing surface at the apex of the return bend, andwherein the planar sensing surface has a maximum length of about twicethe radius of the return bend.
 15. The sensor system of claim 9 whereinthe enclosure comprises a closure base, a closure dome having cableports, a splice tray attached to the closure dome, a means for sealingthe dome to the base, and a means for securing the dome to the base; andwherein the sensor system comprises the sensor, a means for conductingfluid to the sensor, and an absorbent material mounted in the enclosureand positioned to absorb the fluid to protect the cable splice.
 16. Thesensor system of claim 15 wherein the means for conducting fluid to thesensor is an internal groove in the closure base.
 17. The sensor systemof claim 15 wherein the absorbent material is a continuous ring mountedin the closure base between the sensor and the fluid-sensitivecomponent.
 18. The sensor system of claim 15 wherein the sensor is anoptical sensor, comprising:(a) a light source for generating light; (b)a light detector and signal generator for receiving light from the lightsource and for generating variable signals dependent on the amount oflight received; and (c) an optical fiber made of a light conductingmaterial extending between the light source and the light detector andhaving a sensing length comprising a return bend in the optical fiberforming an apex, wherein the return bend has a bend radius less than orequal to about 2.5 times the radius of the optical fiber.
 19. The systemof claim 15 wherein the sensor is an optical sensor, comprising:(a) alight source for generating light; (b) a light detector and signalgenerator for receiving light from the light source and for generatingvariable signals dependent on the amount of light received; and (c) anoptical fiber made of a light conducting material extending between thelight source and the light detector and having a sensing lengthcomprising a return bend in the optical fiber forming an apex, whereinthe return bend has a bend radius less than or equal to about 2.5 timesthe radius of the optical fiber, wherein the sensing length furthercomprises a planar sensing surface at the apex of the return bend, andwherein the planar sensing surface has a maximum length of about twicethe radius of the return bend.
 20. The sensor system of claim 8 whereinthe fluid-sensitive component is an electrical component.
 21. The sensorsystem of claim 8 wherein the fluid-sensitive component is an opticalfiber component.
 22. The sensor system of claim 8 wherein the fluid iswater.
 23. The sensor system of claim 8 wherein the sensor is an opticalsensor, comprising:(a) a light source for generating light; (b) a lightdetector and signal generator for receiving light from the light sourceand for generating variable signals dependent on the amount of lightreceived; and (c) an optical fiber made of a light conducting materialextending between the light source and the light detector and having asensing length comprising a return bend in the optical fiber forming anapex, wherein the return bend has a bend radius less than or equal toabout 2.5 times the radius of the optical fiber.
 24. The sensor systemof claim 8 wherein the sensor is an optical sensor, comprising:(a) alight source for generating light; (b) a light detector and signalgenerator for receiving light from the light source and for generatingvariable signals dependent on the amount of light received; and (c) anoptical fiber made of a light conducting material extending between thelight source and the light detector and having a sensing lengthcomprising a return bend in the optical fiber forming an apex, whereinthe return bend has a bend radius less than or equal to about 2.5 timesthe radius of the optical fiber, wherein the sensing length furthercomprises a planar sensing surface at the apex of the return bend, andwherein the planar sensing surface has a maximum length of about twicethe radius of the return bend.
 25. A sensor system comprising:anenclosure for a fluid-sensitive component; and a fluid sensor positionedin the enclosure for detecting and signaling the presence of a fluidwithin the enclosure, wherein the sensor is an optical sensorcomprising:(a) a light source for generating light; (b) a light detectorand signal generator for receiving light from the light source and forgenerating variable signals dependent on the amount of light received;and (c) an optical fiber made of a light conducting material extendingbetween the light source and the light detector and having a sensinglength comprising a return bend in the optical fiber forming an apex,wherein the return bend has a bend radius less than or equal to about2.5 times the radius of the optical fiber.
 26. A sensor systemcomprising:an enclosure for a fluid-sensitive component; and a fluidsensor positioned in the enclosure for detecting and signaling thepresence of a fluid within the enclosure, wherein the sensor is anoptical sensor comprising:(a) a light source for generating light; (b) alight detector and signal generator for receiving light from the lightsource and for generating variable signals dependent on the amount oflight received; and (c) an optical fiber made of a light conductingmaterial extending between the light source and the light detector andhaving a sensing length comprising a return bend in the optical fiberforming an apex, wherein the return bend has a bend radius less than orequal to about 2.5 times the radius of the optical fiber, wherein thesensing length further comprises a planar sensing surface at the apex ofthe return bend, and wherein the planar sensing surface has a maximumlength of about twice the radius of the return bend.
 27. A sensor systemcomprising:an enclosure; a fluid-sensitive component mounted in theenclosure; and a fluid sensor positioned in the enclosure for detectingand signaling the presence of a fluid within the enclosure, wherein thesensor is an optical sensor comprising:(a) a light source for generatinglight; (b) a light detector and signal generator for receiving lightfrom the light source and for generating variable signals dependent onthe amount of light received; and (c) an optical fiber made of a lightconducting material extending between the light source and the lightdetector and having a sensing length comprising a return bend in theoptical fiber forming an apex, wherein the return bend has a bend radiusless than or equal to about 2.5 times the radius of the optical fiber.28. A sensor system comprising:an enclosure; a fluid-sensitive componentmounted in the enclosure; and a fluid sensor positioned in the enclosurefor detecting and signaling the presence of a fluid within theenclosure, wherein the sensor is an optical sensor comprising:(a) alight source for generating light; (b) a light detector and signalgenerator for receiving light from the light source and for generatingvariable signals dependent on the amount of light received; and (c) anoptical fiber made of a light conducting material extending between thelight source and the light detector and having a sensing lengthcomprising a return bend in the optical fiber forming an apex, whereinthe return bend has a bend radius less than or equal to about 2.5 timesthe radius of the optical fiber, wherein the sensing length furthercomprises a planar sensing surface at the apex of the return bend, andwherein the planar sensing surface has a maximum length of about twicethe radius of the return bend.
 29. A sensor system comprising:anenclosure; a fluid-sensitive component mounted in the enclosure; and afluid sensor positioned in the enclosure for detecting and signaling thepresence of a fluid within the enclosure, wherein the enclosure isnormally fluidtight, the fluid-sensitive component being a cable splice,the enclosure being adapted for mounting the cable splice therein, andwherein the sensor is an optical sensor comprising:(a) a light sourcefor generating light; (b) a light detector and signal generator forreceiving light from the light source and for generating variablesignals dependent on the amount of light received; and (c) an opticalfiber made of a light conducting material extending between the lightsource and the light detector and having a sensing length comprising areturn bend in the optical fiber forming an apex, wherein the returnbend has a bend radius less than or equal to about 2.5 times the radiusof the optical fiber.
 30. A sensor system comprising:an enclosure; afluid-sensitive component mounted in the enclosure; and a fluid sensorpositioned in the enclosure for detecting and signaling the presence ofa fluid within the enclosure, wherein the enclosure is normallyfluidtight, the fluid-sensitive component being a cable splice, theenclosure being adapted for mounting the cable splice therein, andwherein the sensor is an optical sensor comprising:(a) a light sourcefor generating light; (b) a light detector and signal generator forreceiving light from the light source and for generating variablesignals dependent on the amount of light received; and (c) an opticalfiber made of a light conducting material extending between the lightsource and the light detector and having a sensing length comprising areturn bend in the optical fiber forming an apex, wherein the returnbend has a bend radius less than or equal to about 2.5 times the radiusof the optical fiber, wherein the sensing length further comprises aplanar sensing surface at the apex of the return bend, and wherein theplanar sensing surface has a maximum length of about twice the radius ofthe return bend.
 31. A sensor system comprising:an enclosure; afluid-sensitive component mounted in the enclosure; and a fluid sensorpositioned in the enclosure for detecting and signaling the presence ofa fluid within the enclosure, wherein the enclosure is normallyfluidtight, the fluid-sensitive component being a cable splice, theenclosure being adapted for mounting the cable splice therein, andwherein the enclosure comprises a closure base, a closure dome havingcable ports, a splice tray attached to the closure dome, a means forsealing the dome to the base, and a means for securing the dome to thebase; and wherein the sensor system comprises the sensor, a means forconducting fluid to the sensor, and an absorbent material mounted in theenclosure and positioned to absorb the fluid to protect the cablesplice.
 32. The sensor system of claim 31 wherein the means forconducting fluid to the sensor is an internal groove in the closurebase.
 33. The sensor system of claim 31 wherein the absorbent materialis a continuous ring mounted in the closure base between the sensor andthe fluid-sensitive component.
 34. The sensor system of claim 31 whereinthe sensor is an optical sensor comprising:(a) a light source forgenerating light; (b) a light detector and signal generator forreceiving light from the light source and for generating variablesignals dependent on the amount of light received; and (c) an opticalfiber made of a light conducting material extending between the lightsource and the light detector and having a sensing length comprising areturn bend in the optical fiber forming an apex, wherein the returnbend has a bend radius less than or equal to about 2.5 times the radiusof the optical fiber.
 35. The system of claim 31 wherein the sensor isan optical sensor comprising:(a) a light source for generating light;(b) a light detector and signal generator for receiving light from thelight source and for generating variable signals dependent on the amountof light received; and (c) an optical fiber made of a light conductingmaterial extending between the light source and the light detector andhaving a sensing length comprising a return bend in the optical fiberforming an apex, wherein the return bend has a bend radius less than orequal to about 2.5 times the radius of the optical fiber, wherein thesensing length further comprises a planar sensing surface at the apex ofthe return bend, and wherein the planar sensing surface has a maximumlength of about twice the radius of the return bend.